The central objective of this grant is to develop a technique whereby pancreatic islets can be successfully grafted into a large animal model, the Rhesus monkey, who is homologous to the human in terms of immune responsiveness and testicular morphology. The following specific objectives are planned: Specific aim #1: Determine the optimal amount of islets grafted per testis to achieve a physiologic reversal of the diabetic process. Earlier studies have shown that a total of 10,000 islets per kg grafted into the testes of diabetic primates led to rapid induction of euglycemia which was sustained for more that 100 days. But these animals also showed evidence of hyperinsulinemia, suggesting that the mass injected may have been excessive. Male primates will thus be made diabetic and a comparative study done on the effect of specified and variable amounts of islet cells on induction of normoglycemia. The results will be correlated with weight-corrected islet counts in the grafted tissues. Specific aim #2: Determine the optimal organ site for islet transplantation in the primate. Clinical application of islet transplantation will require the grafting of a large mass of islets into the testes. Theoretically this may not be feasible because of the relatively smaller size of the testis of man compared to that of the primate. But earlier studies revealed that the grafting of islets into the testis of rats with concomitant cyclosporine therapy led to the induction of tolerance in the host. A study will thus be conducted in male primates on the survival of islets transplanted into the livers of animals with a primary testis graft, compared with survival of identical preparations in the livers of naive animals who had never been exposed to islets. Specific aim #3: Design a method for the grafting of female monkeys. Previous studies in rats have shown that isolated Sertoli cells grafted along with islets into the renal subcapsular space of female rats led to augmented islet allograft survival. Consequently a study will be initiated whereby the survival of islets, with and without Sertoli cells, will be examined in the renal, subcapsular space of diabetic, female primates. Specific Aim #4: Determine the effect of established intratesticular islet allografts on glucose homeostasis. Using standard methods for the stimulation of insulin secretion from beta cells, grafted primates will be given IVGTT, OGTT, and sustacal stimulation tests. Serum glucose, insulin and C-peptide levels will be determined and compared with control, and with diabetic, non-transplanted, animals. Specific Aim #5: Examine the effects of intratesticular islet allografts on testis and beta cell morphology. Grafted, normoglycemic animals will be orchiectomized and the tissues prepared for light and electron microscopy. The degree of granulation of beta cells, the relationship of beta cells to testicular cell components, presence or absence of inflammatory reactions, are some of the characteristics which will be assessed. The results of these studies will provide knowledge critical to the long term objective of designing and developing techniques for the transplantation of the human diabetic with isolated pancreatic islets.